1. Field of the Invention
The present invention relates to a cross sectional configuration creating apparatus in the creation of a free curve, and more specifically, to a cross sectional configuration creating apparatus in the creation of a free curve for creating a cross sectional configuration for creating a free curve by a CAD/CAM system.
2. Description of the Related Art
This application was filed on PCT international application No. PCT/JP93/00449 on Apr. 7, 1993.
A free curve of a metal mold and the like is composed of a basic curve (BC) as an arbitrary curve and a drive curve (DC) in a spatial coordinate system. More specifically, the free curve is created by moving the drive curve along the basic curve in accordance with a predetermined rule. Therefore, when the free curve is created, the drive curve must be defined with respect to the passing-through points of the basic curve. The drive curve is referred to as a "cross sectional configuration" and usually defined on a plane coordinated system.
FIG. 14 is a diagram showing the relationship between the basic curve and the drive curve, wherein a basic curve BC is defined on a spatial coordinate system (X, Y, Z). A cross sectional configuration DC141 is defined at the passing-through point P141 of the basic curve BC as the drive curve. In the same way, a cross sectional configuration DC142 is defined at a passing-through point P142. These cross sectional configurations DC141, DC142 are curves defined on respective plane coordinate systems 141, 142 each having a V axis as the ordinate and an H axis as the abscissa.
Conventionally, there are known four methods of defining a cross sectional configuration with respect to a basic curve, i.e., a "parallel method", "radiation method", "normal method" and "vertical method" which will be described below.
FIGS. 15(a)-15(d) are diagrams of methods of defining a cross sectional configuration with respect to a basic curve.
First, a method of defining the cross sectional configuration by the "parallel method" will be described by using FIG. 15(a). A cross sectional configuration DC151 is predefined. Then, an operator designates the angles, passing-through points and the like of defined plane coordinate systems in a spatial coordinate system. With this arrangement, plane coordinate systems 151a, 152a, 153a are positioned at the angles designated at the passing-through points on a basic curve BC151. Therefore, a free curve is created from the basic curve BC151 and the cross sectional configuration DC151 on the plane coordinate systems 151a, 152a, 153a.
Further, a method of defining the cross sectional configuration by the "radiation method" will be described by using FIG. 15(b). A cross sectional configuration DC152 is predefined. In addition, a point P152 is designated which serves as the center in a spatial coordinate system. The point P152 is positioned on the radiation having the ordinate (V axis) as a central axis so that the point P152 acts as the origin of, for example, plane coordinate systems 151b, 152b, 153b. A free curve is created from the cross sectional configuration DC152 of the thus positioned plane coordinate systems 151b, 152b, 153b and a basic curve BC152.
Further, a method of defining the cross sectional configuration by the "normal method" will be described by using FIG. 15(c). A cross sectional configuration DC153 is predefined. Next, passing-through points on the basic curve BC153 in a spatial coordinate system are designated. Plane coordinate systems 151c, 152c, 153c are positioned so that the tangential vectors of the basic curve BC153 at the passing-through points become normal vectors. A free curve is created from the cross sectional configuration DC153 of the thus positioned plane coordinate systems 151c, 152c, 153c and the basic curve BC153.
Then, a method of defining the cross sectional configuration by the "vertical method" will be described by using FIG. 15(d). A cross sectional configuration DC154 is predefined. Further, a basic curve BC154a is defined on a plane coordinate system BS154a and a basic curve BC154b is defined on a plane coordinate system BS154b. Next, passing-through points are defined on the two basic curves BC154a and BC154b. Then, plane coordinate systems 151d, 152d, 153d are positioned so that one end point of the cross sectional configuration DC154 is at the passing-through point of the basic curve BC154a and the other end point thereof is at the passing-through point of the basic curve BC154b as well as the line segments passing through the respective passing-through points of the basic curve BC154a become the vertical lines of the plane coordinate system BS154b. A free curve is created from the cross sectional configuration DC154 of the thus positioned plane coordinate systems 151d, 152d, 153d and the basic curve BC154a.
Nevertheless, when the cross sectional configuration is defined, since it is defined on the plane to be positioned in the spatial coordinate system, other line segments such as, for example, basic curves and the like are displayed on a display unit, and thus a problem arises in that the cross sectional configuration is difficult to be defined.